Open-pit coal mining involves directly peeling off the topsoil and a strata overlying a coal seam, so the coal seam is exposed and then exploited. The stripped rock and soil are stacked in layers inside and outside of a mining area, to form a dumping site. A large-size dumping site is an artificially piled giant body formed by stacking the mixed soil and rock in the mining area. During the formation of a large-size dumping site by stacking, the changes in local water level and water quality of the dumping site are critical factors in the regional environmental assessment and in the early warning during the safety production of a coal mine.
The formation process of the dumping site is practically a mining process of an open-pit mine; however, few relevant studies are available now. The water level is investigated by some work teams by arranging several measuring wells in an area around the dumping site. However, this mode of arrangement requires multiple measuring wells, and the cost is high. Moreover, the actual changes in water level and water quality of the dumping site are not determined directly, which is inexact for scientific research, and the changing tread of the water level and water quality from the center of the dumping site to surrounding areas cannot be determined. Finally, real-time monitoring of the changes of water level and quality during the formation process of the dumping site from small to large, that is, the whole process from the mining of the mining region to the formation of the dumping site by mining, is not really achieved at present. However, this data is of great reference significance for scientific research, environmental assessment and early warning in safe production of a coal mine. The dumping site of the open-pit coal mine has the characteristics of “heavy rain, serious slippery; light rain, moderate slippery; and no rain, no slippery”, so it is very important to monitor the change of water level in the dumping site in real time, as far as the stability of the dumping site is concerned.
The difficulties in real-time monitoring of the changes of water level mainly include the following.
1. During the formation process of the dumping site, the ground surface is elevated from low to high, and thus the height of the measuring well will be gradually increased dumping site. It is a difficulty to realize the safe and stable increase of the height of the measuring well, and ensure the stable measurement and transmission of the data.
2. The dumping site mainly includes two regions in a longitudinal direction. One is an aboveground region that is a stacking site. The water in this region is mainly replenished by surface water, and the changes of water level is high and greatly affected by the weather, and has important impact on the safety of the dumping site. The other region is an underground region, and the water level in this region is affected by the drainage of the pit, and directly correlates with the drainage and gushing-out of water from the pit. The water quality is also an important reference data.